DE2824320A1 - METHOD FOR PLATING LIGHT METALS IN THE PURPOSE OF INCREASING LATERAL CORROSION RESISTANCE - Google Patents

Description

Process for the plating of light metals in order to increase the lateral corrosion resistance

The invention relates to a method for plating light metals to increase the lateral corrosion resistance.

In general, the teaching of the use of aluminum with a content of 1 to 8% zinc as a substrate and the use of a pretreatment with a brass layer with a content of 60 to 75% copper are proposed in the context of the invention. This results in an increased lateral corrosion resistance of the clad system on the light metal, in particular aluminum.

Considerable attention is paid to weight reduction in automobile design for the purpose of energy saving. In the case of automobile bumpers, it is necessary to reduce the weight and the government regulations for bumpers are increasing meet without sacrificing the durability, the appearance, the cost-effectiveness and the stylization variety of the nickel-chrome plate ation is harmed.

The invention is concerned with a clad aluminum product and a method of making the same Product, for example for use in motor vehicle bumpers. To get plating adhesion, you have to

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Aluminum substrate in alloy form with a content of 1 to 8 % zinc. An outer decorative plated coating is applied and is preferably comprised of chrome (0.000012 to 0.00012 cm (.000005 to .00005 ")) on nickel (0.0007 to 0.0075 cm (.0003 to .003") )) · An electroplated pretreatment system is used between the outer protective coating and the aluminum alloy, which essentially consists of at least one brass layer with a deposited copper content in the range of 20 to 75 % for the purpose of adhesion. In order to obtain increased lateral corrosion resistance of the entire coating system, the substrate must preferably be limited to a zinc content of 4.5 to 5.5 % and the brass layer must contain 60 to 75% copper as deposited. The lateral corrosion 3 of ^each layer of the coating system is thereby practically reduced to zero, so that any corrosion is limited to microneedle holes perpendicular to the plated surface, these pinholes not damaging the decorative appearance. The pretreatment system can be expanded to include a copper layer enclosed in two layers of brass, the first layer closest to the aluminum substrate must contain 60 to 75% copper and the second brass layer closest to the decorative coating can contain 50 to 60% copper. In this extended system, the second layer of brass has a controlled type of side corrosion to prevent blistering and is damaged to protect the other elements of the system. The plating solution for performing brass plating is designed to provide increased coverage and dispersion and may specifically contain 27 to 73 g / L (3.6 to 9.6 oz./gal.) Sodium cyanide, with the ratio of sodium cyanide to metal being 1 , 2 to 1.6 times the metal, 15 to 28 g / L (2 to 5 oz./gal.) Sodium hydroxide, 30 to 92 g / L (4 to 12 oz./gal.) Sodium carbonate and a total brass metal content of 22 to 45 g / l (3 to 6

809849/1002

oz./gal.), which are divided into a content of 68 to 85 % copper and 15 to 32 % zinc. The zinc or copper elements are in principle added to the solution as cyanide, but can also be present in small amounts as oxide or can be derived from the electrode.

Theoretically, it is believed that improved adhesion is achieved when the cleaned selected aluminum alloy substrate is exposed to this solution under current, wherein the etchant chemically dissolves some particles of the substrate releasing zinc for immediate coating, the rate of chemical conversion slightly of the electrodeposition of Brass precedes it. Theoretically, it can further be assumed that if at least the first plating deposit consists of brass with 60 to 75 % copper, a favorable brass alpha phase results which critically controls the electromotive potential of the plating and thereby also the resistance to lateral corrosion .

The high strength aluminum alloys currently available hold the promise of advances in reduction the weight of the bumper system while complying with government regulations for impact resistance of bumpers. However, prior to the present invention, it was not possible to (1) one on an industrial scale Electroplating permanently adhering metal plating directly onto aluminum, especially a brass plating, and (2) to obtain a bright, shiny coating system for an aluminum substrate, which at most has minimal lateral corrosion suffers. This is due to some problems including the natural oxide film that forms on the Aluminum is present ^ and this is due to this oxide film in achieving a strong bond between any clad material over the aluminum base caused disturbance. If the natural oxide film is

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as would be removed and replaced with a clad system, the natural corrosion resistance of aluminum becomes damaged and the clad materials would be a potential galvanic element in a corrosive environment Surroundings. With such an element, aluminum is the Anode and shows the tendency to dissolve. Since aluminum is more reactive than steel, the rate of dissolution will be actually faster than with steel bumpers.

The behavior of clad aluminum can be determined by a pre-plating treatment or a backing system, both of which are included below as pretreatments will. Over the years a number of pretreatments have been suggested, mostly addressing the problem of the Achieving a high level of adhesion were directed. Very few have been successful, and even these only marginally Extent. They include (a) a chromium-on-nickel-on-copper system on zinc on aluminum, typically referred to as the zincate process, (b) a chromium on nickel system Bronze on tin on aluminum, which is typically referred to as the Alstan process, (c) a chromium system Brass (high zinc content) on aluminum, which is known as the Dupont process, a system of chromium on nickel an immersion zinc layer (which dissolves to a certain extent during immersion in the nickel bath) on aluminum, referred to as the Alcoa 661 process, and (d) a Phosphoric acid anodizing treatment using a system of chromium on nickel on anodic oxide on aluminum. Each of these systems are deficient in that they either fail to achieve adequate adhesion or are overly galvanic Create elements that accelerate corrosion between the various elements of the system.

Most of the previous top coating systems for decorative use, such as nickel and chrome, have been used developed on mild steel substrates and found there

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special application ·, the top coating systems were subsequently transferred for use with aluminum in the hope that their behavior would be comparable. However, it had to be established that there are different physical parameters, when a plating system is applied to aluminum. An electromotive force can be between all of the elements of these cladding systems are present when bonded to aluminum that are not present when they are connected with steel. The natural oxide coating on aluminum inhibits firm adhesion of the plated system. Without proper adhesion, the type of galvanic element in between can be due to the change in current flow between the electrolyte of the galvanic element and the special metal that forms the poles of the element is increased or decreased will. Although stainless steel, for example, is far more noble than copper, for example, its effectiveness in galvanic engineering Element considerably larger due to its high resistance to current flow through its interface with the electrolyte. As a result, plating systems for steel substrates must be careful because of the unpredictable Art can be analyzed in the application of such systems on aluminum and still do not achieve any comparable ones Results regarding adhesion and corrosion resistance.

In a separate area of technology and in attempts to lower the amount of electromotive potential between the elements of the system in the hope of improving lateral corrosion resistance, brass was introduced in two known instances in the art for use in steel plating. In the first case the brass was constructed to contain a high level of zinc, about 70% , with the copper being kept at about 30 % . If this application of brass were applied to an aluminum substrate, zinc as a highly reactive metal would be consumed and the corrosion would be severe

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advance rapidly laterally in the brass layer, so that peeling and blistering would be formed under the decorative coating. In addition, the system would be undesirable Immersion coating methods are limited as such a brass has permanent adhesion to aluminum is not possible by electroplating according to the prior art.

In the second case it was required that the electromotive potential of the brass be increased so that it lies between steel and nickel. Any galvanic formed element would lower and therefore slow the rate of corrosion. This was achieved by increasing the copper content of the brass to 45 to 60 % . If this concept were applied to an aluminum substrate, the electroplating adhesion would still remain a serious problem and the galvanic element between the increased copper brass and the aluminum would be larger than on steel, the brass would not be able to provide the preferred cathodic protection to supply for the outer decorative layers.

A pretreatment is therefore necessary, which (1) a constant good adhesion of the electroplated elements on the aluminum and (2) the potential of the galvanic element between the aluminum and the neighboring one Layer decreased.

A main object of the invention is to provide an economical and easily controllable coating system for high strength Aluminum alloys, this coating system providing a glossy decorative finish, a high degree of Shows adhesion of the cladding system to the aluminum and offers increased lateral corrosion resistance.

809849/1002

Another object of the invention is a pretreatment for a glossy coating for application Aluminum substrates that are exposed to a highly corrosive environment, e.g. as bumpers for motor vehicles, whereby the pre-treatment system avoids large stress elements which cause corrosion between the elements speed of the plating system and / or with the aluminum or glossy finish.

Another object of the invention is a method of plating and forming a plated system for high-strength aluminum alloys that provide a previously unknown strong bond with the aluminum substrate without there is a need for complicated cleaning or pretreatment steps.

Another object of the invention is a plating system for aluminum, which has a high gloss decorative finish with a reduced amount of plating · materials.

Another object is to provide a method of pre-treating aluminum bumpers with a minimal capital investment and taking advantage of the facilities normally available for cladding steel.

The features with regard to the above objects include (a) the use of an aluminum alloy substrate with a content of 1 to 8% zinc, the zinc intermetallic compounds in the substrate during the treatment form a firm intermolecular bond with the selected materials of the pretreatment system, which especially brass as Must contain an initial layer with a copper content of 20 to 75 % , (b) the avoidance of lateral corrosion within the clad system by using at least one or all materials (i) a recrystallized aluminum

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minium alloy, (ii) an aluminum substrate with a content of 4.0 to 5.5% zinc, (iii) formation of the metal layer in contact with the substrate to a content of 60 to 75 % copper, the remainder zinc, (c) formation of a Brass pretreatment plating solution of cyanide compounds with a high copper content, the solution containing graded components to provide better dispersion and tightness of the clad material, for example maintaining the ratio of sodium cyanide to metal in the range of 1.2 to 1.6 times the metal and Avoidance of arsenic contamination above 0.0001 wt.%, (D) Ensuring a controlled type of corrosion practically limited to microneedle holes in a perpendicular orientation to the clad surface, or controlling the corrosion by allowing a slow rate of lateral corrosion in an intermediate layer Development of a copper pretreatment layer in two layers made of brass, the brass layer adjacent to the aluminum containing 60 to 75 % copper and the layer adjacent to the decorative plating system containing 50 to 60% by weight copper, (e) the retention of a bright, shiny decorative finish by using shiny copper or copper and nickel as an undercoat for the nickel and chrome cover layers, while at the same time the corrosion protection is promoted by covering this copper or copper and nickel layer with brass with a high copper content, and (f) restriction of the cleaning and plating processes to those that are necessary for the plating of steel are interchangeable.

Put in the drawings

1 is a graphic representation of various previous coating systems on aluminum and the coating system according to FIG of the present invention,

FIG. 2 is a graph similar to that of FIG

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Fig. 1 for the previous iberzugasyofccao cxvx steel or

the FIf ;, 3 u ..: d 4 sclic-ia troche Dicg ^ cr-i-iO dor RoiLeiifol ^ o (Lev Corrosion _ if eic dui'cli ο in known about;.: r.3c. "yGten, Czc els ZiiiliutbcLinung boioiclno !: vlrd, foroüciii'üioct,

clic Fig., S 'vrd 6 f, v? p: iincli das For oscliroitcn der Ilorrocicn for a vji-lc'oz bcliamiucc Uboi'zr ^ a ^ yübcm, daa iiblichcr;.' GicD εΐε Alctaii'-VorfcIirCii bor; oicl :: iOw \ .- li ~ d,

the Fig, 7 u-id C dc; i Fortccliri'oc dor corrosion for a about-2U _v 7323 "- !, cn {cuLIß dor present egg-xindu-ij ^

the Fif, S c: Li: c F-iotc ^ rapliio of Prebrn, to the CASS-Tcci'c cx.zgosctz'c \ ~. "Cc ^ Xj \: otoi the specimens variiorc-.vlo o]> 3O3cliicdcnQ liv. ~ x ~ Tßchcl-l ^ in dor exit an Alunixiiuulcgierung 7029 on ^ o-

own

the fi; c. IG hin 17 öcvoils Ilikropliotograpliien of specimens, volcL rer.: Sweet of the invention u- ^ d extralialb dc3 ralauons of the inventions herjGivcllt irirdcn, which show the foreground or absence of bubbles or other kinds of corrosion defects,

In the context of the description of the invention in detail, this concerns itself with the use of aluminum or iliacumin as a fine substrate, x; orcuf a shiny, bright decorative metal finish, which in typical v / o ico consists of oligol and / or clrcn , plated 1st. Sot; ohl Aluninium as well as Hagnociun zoigCii in different degrees the same problem of the Haftu cinoG clad SyctcmoG because of their own protection cigenGchaftcn. Similarly, both show the same galvanic corrosion problem as they are comparable in the cioktromctoriGchon range and show similar galvanic elements with regard to different types of plating systems that have already been used. If aluminum is referred to below, magnesium is also included, unless otherwise stated.

8098A9 / 1Ö02 _ΜΛ1

BATH ORIGINAL

With aluminum as substrate nut dor Unwell ι: ίο.Ί ci "c :: i brightly shiny; decorative outer plate" * ^T .rig, ';cy3L;:::; t and el la necessity of a procedure with nicd;? I ^ c λ J'oGbcn 11 '.? Ccd coating systems in the ancestors cine aviigor.zoichncto Kaftv.:~j and low lateral corrosionGcigciischaftci orroiclit 'be.

liability

The direct current electroplating of liotall directly on aluminum is not technically successful v.:id only one direct plating of Chrin in the earth negative. Ilcistcns will the electroplating on aluminum in the technical Practice using a chemical dipping ink layer made of zinc, usually named after the Zinkatvori'alircii is applied, or carried out by applying other immersion layers of bronze or tin. The gc ;; L "iltcn egg:? .- dip layers, for example au3 Zink, Iicssing, Z; i "IJi and Tin chemically replace the oxide film on the aluminum, which then provides the basis for the adhesion of a plating of other metals. The immersion procedures are more of a mystery as a science since actual Ilcclianism liability cannot be understood and undesirable variations occur. Other metals even adhere to the immersion processes not, such as winding, copper and iron.

The difficulty of plating on aluminum is intense examined by Schwartz and Ncwkirk at the University of Colorado, 1972, and they found fcsb that a DC plating on aluminum with the cheapest plating metals such as nickel or copper-lead was not possible. DuPont's Svendalah also studied DC plating in 1974 from brass to aluminum. and concluded that the electrolyte must be adjusted so that the plating consists practically entirely of zinc before good adhesion is achieved, whereby he assumed that a certain kind of

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BATH ORIGINAL

Ir ^- TI ¹ Hr co :; Gjcidfj.lmoc occurs. The attempt by DuPont vr-i '' ¹ OUTti't practically the zinc immersion process. This is very much a disadvantage, since the plated mossing with! ■ eh '·.! ^/: Nkgr> just slightly in the subsequent acid dips or Flattierungsb ^ dera attacked and wrong vcrdcn necessary to plate nickel, if it is not protected by additional locking elements.

According to the invention, it was found that a good llafivn. In reliable V. ^r e.iso can be obtained by direct current plating of '- r.rring directly on aluminum, vorr: ir - .: c5ctzt, that the Alumiiiiumsubstrat is selected to (ai> ι ^::;; contains up ο% alloyed zinc, and brass ■ - '} c:.. A rolyi "is not only configured so as brass with Ri.I -vT 1- ^ ·; .Γ "ΌΙι11ίΓ: · οη cure content from 26 to 75 % cut off-C '- * -, Ec.-ir'f rn also contain cr-sro-related caustic elements ¹ " ., "v / clcho lc'rcix the Oxid'iln and einon part of the aluminum is s angeno.T.nen that on entry of the Messingcl '··:.' .rolyts ΐ in con current lot alloyed zinc in the Occi The aluminum object is distributed v / iiv.:; C '. ^: Ai? A zinc-rich Zv / ischenbereich forms in the floor, which favors the adhesion of the brass. Fs the phenomenon occurs that the zinc is only from dom Substrate f _: ozen v / ird, in order to obtain a more compatible crystal structure e.g. u favor, which unites the substrate and the PIeLtiorung. In the absence of alloyed zinc in the c "c- !:" object together with some zinc or increased zinc in the brass electrolyte, there is no improved adhesion. In addition, the brass with a high copper content does not become in the subsequent acid immersion baths or plating baths that cause flatting are necessary by nickel, so that no intermediate barrier layers need to be applied.

809849/1 002 ORIGINAL BATHROOM

The preferred method of practicing the invention i :; '; the following:

1) A kneaded or extruded AUirniniu:.]; Jc. ": R_: · Stand or aluminum substrate with 1 to 8 ^c / o alloyed zinc is used; smaller amounts of alloyed zinc deteriorate!: .- ¹ , the adhesion and larger amounts of zinc undesirably affect the physical properties of aluminum.

2) The aluminum object is given the following Rcinigvags- and subjected to activation process, whereby foreign material and Remove the oxide film from the object:

(a) It is in a weakly alkaline cleaning solution even during 1 to 4 min INPØ at 60 to 85 C ^r / oicht and with a similar alkaline solution of 40 to 55ΓΠ str ^ vi! ¹ - sprayed.

(b) The article is vcu in another alkaline Wasccvlösung, preferably with a content of 68 ^c / o lMatrii ^ n ^ '■ _. dioxide, at least 0.5% Trinatriu.nphosphat, 15% IJatriu. ::. ¹ metaphosphate and a maximum of 10 Jo IIatriuDcarboiiat> etched.

(c) The object is cleaned in a sulfuric acid solution (2 bin '!. VoI- ^ o) with added fluoride salts and / or V / asscrstc :. " : peroxide, with a water rinse of Raunte ::".; temperature on the object after soaking, dvi:.: etching and the cleaning stage is applied.

3) The cleaned and etched article is immediately fed to a DC plating cell, the article being placed as a cathode to face the opposing star. ing a thin measurement layer (0.00012 to 0.00025 cm (.00005 bi ;; .0001 inch)) to be plated, copper Vo i which 26-75 wt: contains n-deposited.. The electrolyte consists of a cyanide solution and shows the full plating voltage the moment the object enters, the plating should last for 3 to 10 minutes at preferably 3 to 5.5 A / dm '"(or operationally 2 to 6.5 A / dm (30 to 50 or 20 to 60 amps./ft)) as the average current density.

809849/1002 _bad0R1G inal

The electrolyte should preferably contain:

15 to 38 g / L (2 to 5 oz./gal,) sodium hydroxide 30 to 90 g / L (4 to 12 oz./gal.) Sodium carbonate

27.5 to 72 ^ 5 g / l. (3.6 Ms 9.6 oz./gal.) Free uatriuncyanide

22.5 bii3 h'j g / l (3 to 6.0 oz./gal ..) Hebauelemente, in ¹ ;.: Divides between copper and zinc in the ratio of 68 to 85 ^C A Kupier and 52 to 15 ^c / i Zinc, whereby the ratio between uranium cyanide and ilotall is 1.2 to 1.6 times the amount of metal.

Finige Tcstbcispiolc prove the layering of the alloyed zinc in the aluminum alloy substrate and the copper content of the brass to achieve the flattening. The Probo production be .et and different approaches in their choice of Aluminiumlegicrungsblcchen (etv / a 10 χ 10 cm) including värmobehandclbaro and non-alloys and värmcbehandclbare

(a) Roughening one side of each sheet (in the case of Clad materials only roughened the bottom half ),

(b) application of acetone to remove the abrasive joint,

(c) Soaking and brushing each sheet clean in a 71 ^C C solution containing 60 g / L (8 oz./gal.) of a powdered additive of 2.5-3.5 Gev / .Jo sodium metasilicate, 17.5 up to 18.5% by weight of sodium pyrophosphate, 31.0 to 32% by weight of sodium tetraborate, 0.5 to 1.5% by weight of surfactants and wetting agents and 23 to 24% by weight of complex organic materials had been produced,

(d) flushing,

(e) soaking in a solution of 71 ⁰ C for 1/2 min, the solution by application of 60 g / l (8 oz./gal.) of a powdery additive of 68% sodium oxide, from 15 to 20 °, i Sodium metasilicate, a maximum of 0.5% trisodium phosphate, a maximum of 10 % sodium carbonate, the remainder sodium hydroxide and a maximum of 3.5 % moisture,

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(f) flushing,

(g) renewed soaking in a solution according to (e) at 71 ⁰ C for 1/2 min,

(h) flushing,

(i) Immersion in an aqueous solution of 50 % HIlO ^ during:.! 15 see,
(j) flushing,

(k) Introducing into the electrolyte of a IIodGingplatte cell with the current switched on, using the sheet metal as cathode, average current density about 3.7 A / da (35 ASF), the electrolyte consisting of 44 g / l free ITaCII, 18 g / l NaOH, 61 g / l Ka ₂ CO ₃ , 22 g / l Cu and 11.2 g / l Zn. Plating was carried out for 4 minutes. In the isolated state, the Kupforgchalt of the IlosningG οΐ ;; α 57 %. The copper content of the Hessing was varied for certain specified samples,

(1) Rinsing (if adhesion, plating was carried out for 9 minutes, it was only checked visually), (m) each sheet was placed in an acidic copper plating column with applied current for 5 minutes to plating a copper layer over it,
(n) flushing,
(o) the liability was qualitative through

1) Tap with a coarse file

2) sawing

3) bending the sheet by folding it back on itself (180 ° bend)

examined.

The results of the tests shown in Table I clearly show that with aluminum substrates with a zinc content of 1 to 8% (see Table II) the adhesion is excellent λ / urdc, regardless of the other alloying elements.

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$ 0

Table I.

Sheet metal alloy

2024 2036 3003 3105

4343

5457 5557 6061

Reflectal R-5

Ford cast alloy

Ford cast alloy

7046

7075/7072-plated

4343/7072-plated

7178 7075 7016 7029

Visual examination of the liability after the inspection

looked good no liability no liability

Blistering and peeling on the Al

Blisters and peeling on Al

Peeling on Al Peeling on Al

very strong blistering

Peeling on Al Peeling on Al

Peeling on Al

looked excellent looked excellent

looked good on 4343 and looked good on 7072

looked excellent looked good looked excellent looked excellent 3-test adhesion test after copper plating

Blisters and peeling no adhesion no adhesion bubbles and peeling

Blisters and peeling

Peeling Peeling Poor Adhesion

Peeling Peeling

Peeling

excellent excellent

peeled off on Al on 4343, the exam was excellent on 7072

excellent excellent excellent excellent

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- Mr-

Table II

Chemical AIu.-
Alloy
tion Si Nominal analysis Mn (Wt.? O, except Al) Cr Ni Zn Ti - - ί - ! 2024 - Cu - Mg - - - - ι
ι - 2036 - 4.4 0.25 1.5 - - - - - ο, 3003 - 2.6 1.2 0.45 - - - - _ I 3105 - 0.1 0.6 - - - - - 1 - 4343 7.5 - - 0.5 - - - - - 5457 - - 0.3 - - - - - - 5557 0.1 - 0.25 1.0 - - - - - 6061 0.6 0.15 0.15 0.6 - - 0.25 - Reflectal
R-5 cast
alloy - 0.3 - 1.0 - - - - Ford 332-
alloy 9.5 - 0.5 0.5 - - - - Ford 103-
alloy 9.5 3.0 0.5 1.0 - - - - 7046 0.1
Max. 3.0 - 1.0 - - 4.5 0.06
Max. 7075 - 1.0 - 1.1 0.26 - 5.6 - 7072 - 1.6 - 2.5 - - 1.0 - 7178 0.5 - 0.3 - 0.3 - 6.8 0.2 7016 0.1
Max. 2.0 - 2.7 - - 4.5 0.03 7029 0.1
Max. 1.0 - 1.1 - - 4.7 0.03
Max. 0.7 1.6

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2S2432Q

Soitliehο Corronion

In Fig. 1 cind graphically relevant extension systems for aluminum summarized, as they have been used up to now; In comparison, two embodiments according to the invention are also shown. Three of the previous systems (Z-1, A-1 and Λ1-2) used immersion coatings or chemical conversion coatings to achieve adhesion to aluminum. Z-1 is: a teclanisches zincate process, which is dealt with in detail below; A-1 is a common tin bath system which gives difficult process control. The Al-2 system is also known as the Alcoa 661 process and presents difficult problems of dissolving the zinc coating in the nickel treatment bath. The ON-1 process or the anodic oxide process does not give good tight adhesion of the coating system. The Du-I (DuPont) process uses an electroplated white brass layer containing about 90 % zinc, such an I-brass layer favors significant lateral corrosion, since natural zinc is quite damaged.

The relevant known plating pretreatments for use on steel are summarized in FIG. There is little problem in achieving good adhesion to steel and direct DC plating from cyanide solutions is common. Copper or nickel have been used as an interface layer with steel. However, copper and nickel do not adhere to aluminum with plating. Thus, the plating technology used for steel cannot be transferred to aluminum. The brass interlayer of the known system P-1, even if it contains 60 to 75 % copper, does not show the same protection against corrosion that is obtained when the brass is bonded directly to the steel.

It should be noted that aluminum in itself is quite

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is resistant to corrosion due to dos from "a natural O; ^cidi% ilin resulting protection.:. lrrb Iiach the Platticrung but enjoys the aluminum these natural SCIM"^1; -. no longer. Clad aluminum is part of a potential galvanic element. Alurilnium ο divides the anode in most of the galvanic elements there:. "* Ur.d tends to dissolve, except with zinc-rich layers, for the time being ...?. The aluminum is cathodic. Since aluminum is rccJ'-tioiiafUhi ^ cv than steel is the speed of dissolution actually: faster than with steel.

are
The other metals / less reactive and generate toi the plating hydrogen gas; this is the electrolyte solution, which consists chiefly of water with common salt and sulfuric acid as the conductive ionic ion. The relative rate of corrosion is partly related to the voltage of the galvanic element. The voltage in turn depends on the reactivity of the metals involved.

A well-known process that addresses the galvanic corrosion problem shows is that of the zincate process, where after a suitable cleaning of the aluminum substrate an immersion layer of zinc typically to a thickness of 0.0000025 to 0.000012 cm (.000001, to .000005 ") (see Fig. 1) is applied. After rinsing, eiiio Copper layer electrodeposited over it and then the decorative coating of nickel and chromium Nickel is about 0.0025 cm (.001 ") thick. The zinc is the most troublesome and vulnerable layer. Zinc becomes boi easily Acid treatment stages attacked and dissolved, in which Nickel or acid copper plating can be applied.) therefore some barrier deposition, e.g. made of thick copper, is necessary, at an additional cost caused.

8098A9 / 1ÖÖ2

Di) / -'- 1 ¹ T-OdC eats electrically connected to a very effective [• -'nßijrcizci-i cathode from rupfor. As soon as the crystalline solution reaches the zinc layer through a small crack (see FIG. 3), the latter preferentially dissolves. This is done very easily, colbst with a gcri ^ go.a scratch or Iladolloch in plated coating. The KorrosiciiseoGchvindiglroit ninmfc is gradually increasing. The surface of the zinc anodo only eats the thin edge of the zinc the circumference of the circle increases. In this case, a clearing effect occurs. The anode-to-cathode ratio falls steadily, which means that the rate of corrosion is progressively increased. If zinc is practically reduced or removed from the area, corrosion does not stop. The Kupfor-Aluniinirraolcmcnt is known for the corrosion of aluminum. Substantial dissolution of the aluminum takes place as long as ali3 fresh electrolyte is available. The depletion of the electrolyte is practically the only delay factor in the galvanic element. If the cladding is ductile and does not break due to the build-up of the corrosion proGi'cto, possible on / off corrosion may occur. Usually, however, the corrosion products progress to such catastrophic proportions that peeling and blistering of the clad system occurs. As a result, the clad ilatorial (see Fig. 4) is slightly raised, invisible, voluminous corrosion products below the cladding and the corrosion products are separated out from the cracks and the aluminum base may be weakened.

In Figs. 5 and 6 there is a further known plating system shown which was applied to aluminum, whether-

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There has probably been some success with regard to the Platt <.o:; i; _ :, 3 of steel. Dien is oi-.i ε.ν.3 oijioi- αϋ: .ic: i immersion layer of tin and a scliiclrb from Broiizo (0.000025 cm (.00001 ")), yj.cdorua preceded by an IJickchroraplattierung connects, existing system. If d; lo Corrosion occurs as a result of a small rica, scratch or! Blemish hole, the corrosion creeps up, dji », cj: i: ■ right to the aluminum surface, away and vcmi it reaches the aluminum through a break in this coating, wii \ l a galvanic element directly between the Altr / Jiraiv. ■. and the bronze. The flUcIiG of the cathode is cnfLii ^ lici limited to the circumference of the Iladellochcs. This is true bo> especially with chrome as the top layer. The corrosion came progress practically indefinitely., However, the AncJc: i- · Cathode area ratio larger. The potential gradient in the galvanic battery is also missing, since aluminum and bronze pretty close together in the Reckti " vitatsskala, so that the corrosion risk / indickoit is slightly lower. However, the corrosion will proceed as the aluminum dissolves, creating a Forms undercut area below the bronze. The speed of the attack around the perimeter of the hole determined in the depth of the used metal Jo Unit time, falls off. The cathode consists mainly at the beginning made of nickel, but is a bronze layer in the direction of the edge released. As the corrosion progresses and the undercut continues to develop, it becomes more and more bronze-plated nickel is released so that the cathodic gradually becomes more effective and the corrosion is increased. This system allows the substrate to be attacked directly and left unprotected.

In the case of an anodizing process for plating aluminum, nickel remains as the cathode regardless of how far the corrosion has progressed. The corrosion

809849/1002 bad original

2B24320

ge π clr beef igle ο it is reduced a little. Jodoch is the bottom of nickel r.iit the bottom .aurs aluminum by dio Form of the O ::: Lds connected. Dor Uachtoil of the procedure lic ^ fc in that the plating adhesion is poor. Corrosion products build up and loosen the plating and off this occurs, more of the cathode is exposed and dia Corrosion accelerates.

From the known methods at hand, it follows that that a favorable or toleriorbaro corrosion is one, t-jolcl: .. (a) crawls through a plated system and advances itself limited to a small pinhole, (b) never by a layer adjoining the aluminum substrate the system advances and (c) minimizes any galvanic element with the aluminum, to delay the decay of the supporting substrate. Qa3 The zincate process fails because the corrosion runs along the sides of the layer adjacent to the aluminum advances? the Tin-bronze pretreatment fails because a galvanic element that is too high is set up with the aluminum, the one cause considerable eventual decay. The anodischo Oxide processes fail because the pretreatment does not adhere closely to the aluminum. Indeed, the corrosion mechanism must through an economical, inexpensive one. Electroplating pretreatment process controlled v / grounding, which is the opposite of these three known embodiments.

Due to the present invention, the defects of the prior art discussed above are eliminated by

(a) the alloy content of the aluminum substrate is controlled to a content of 4 to 6% zinc or a recrystallized aluminum substrate with 1 to 8 % zinc and

(b) a thin layer of brass is electroplated directly onto the aluminum article, the layer containing 60 to 75 % copper to avoid lateral corrosion along the interface with the article and to ensure a tight bond

809Ö49 / 1ÖÖ2

- 22. -

to favor and sour Bchandlungsstufcn, \ / io the placement of the nickel ^ to enable directly on this. The plating system is shown to the greatest extent in FIG. 1 and is designated as embodiment A according to the invention. The thicknesses of the clektro-deposited layers should be approximately: brass 0.00025 cm (.0001 "), winding 0.0025 cn (.001 ") and chrome 0.000012 cm (.000005"). Dor reason for the high resistance of this system to lateral corrosion dos brass3 is not entirely an hourly. Nevertheless it is assumed that the atomic bond is broken aluminum and brass are such that vertical corrosion is forced in the substrate between the brass and Aluminum is present, which one favors this bond and of course the galvanic elements the constituent? of the system changes. The aluminum will be attacked at a very slow rate and the appearance will not affected, as the small pinholes are white corrosion products release and avoid peeling or blistering.

An alternative plating system according to the invention is shown in FIG. 1 as embodiment B and in FIGS. A copper or winding and copper layer 10 (0.012 cm (.005 ")) is contained between two brass layers 11 and 12, the first layer 11 having 60 to 75 / J copper to prevent lateral corrosion at the interface to avoid the aluminum substrate, while the other layer 12 in the deposited state has 45 to 60 % copper, in order to allow slow controlled damage corrosion for a longer protection of the aluminum.

The copper 10 is pure copper and the brass layers are electrodeposited from brass cyanide solution. That electromotive differential potential between nickel and the brass layer 12 is relatively low and the polar i-

809849/1002

siermigccigenschnft of ilessings 12 is good that you the low voltage potential does not shift significantly and allows a slight current flow. As a result, the corrosion of the ilining layer 12 becomes the Undercut nickel; This takes considerably longer than any of the heretofore known ancestors and during this period, both the copper and brass protect 11 da3 aluminum. If the brass 12 is corroded, there will be substantial penetration through the copper or copper and nickel layer 10 appear. If the corrosion is caused by the second layer of ilessing 1.1 is to progress, the galvanic element between the brass 11 with high copper content and the aluminum is relatively low in favor of corrosion, which, if at all, occurs at a slower rate progresses. The layer 11 suffers at most a very long consuming corrosion (side corrosion) to the above Cu; this is essential to control the corrosion to be perpendicular and least of all detrimental to the appearance. The corrosion progresses through the copper and brass in a practically vertical direction continues, limits the products of corrosion and prevents the clad layers from sagging or rupturing due to blistering and lack of adhesion. A preferred method of embodiment B is detailed given below:

1) A recrystallized aluminum substrate is selected and applied which is of the 7000 series containing 4 to 6 yo of zinc.

2) The aluminum alloy is dipped to a rough to obtain general surface cleaning. This soaking treatment can be carried out in three phases, (a) Soaking in a weakly alkaline cleaning solution as in the case of the test examples dealt with above Step (c) for a period of 1 to 4 minutes at a

809849/1002

-2A-

Temperature from 60 to 85 ^C C, (b) jet spraying the aluminum substrate with a similar weak allzalicchc:?. Cleaning solution, as according to (a), for a period of 1 to 3 min at a temperature of 40 to 55 ^C C, vo ". :: ol the jet spraying is carried out by applying the solution CJ - the aluminum substrate with a force of about 1.2 atmospheres (16 psig) and (c) rinsing dos oingeuoiclitcii and sprayed substrate with water for a period of 1 min at room temperature.

3) Treatment of the soaked aluminum substrate with a mild etching cleaner to produce a uniform CIDi ^ cn etching of the aluminum surface. The etching solution is an alkaline weakly or non-silicatizedo Elektroroiiiijir.ij;?. solution or a similarly formulated alkaline solution, dio a uniform etching on the surface provides, Worni the aluminum is treated min during a period of 1 to 3, wherein the solution is maintained at a temperature of about 40 to 7O ⁰ C. A preferred solution preparation can include: addition of a powder in an amount of 45 to 82 g / l (6 to 11 oz./gal.) Of water, the powder additive containing a maximum of 3 to 5 % moisture and 3 powder 68 % sodium hydroxide, contains a minimum of 0.5 % trinatriunphosplint, 15 % sodium metaphosphate and a maximum of 10? S sodium carbonate. The aluminum is then subjected to a water rinse to remove the products of the weakly alkaline etching solution, the water rinsing being carried out for about 2 minutes at room temperature.

4) The etched and soaked aluminum alloy is uring peeled off by dipping or sinking in a weakly acidic solution v / a period of about 1 min, wherein dio solution in the range of 15 to 27 ⁰ C held v / ill. The preferred draw solution may contain 2 to 12 vols. Sulfuric acid with added fluoride salts, for example 2 g / L (0.25 oz./gal.) Ammonium bifluoride and / or hydrogen peroxide.

BATH ORIGINAL 8098A9 / 10Ö2

The products of this trigger treatment are dipped rinsed in water for 1 min at room temperature.

5) A layer of Hessing is electrodeposited onto the aluminum substrate produced in this way, for this purpose the object is immersed in the electrolyte with the full plating voltage applied, the average plating current density being about 3 to 5 A / dm (30 to 50 amps./sq.ft.) . The electrodeposition while 3 to 10 of the electrolyte of 21 min at a temperature up to 32 ⁰ C (AO to 90 ⁰ F) is carried out, so that a layer having a thickness of about 0.00025 cm (.0001 ") is obtained. It is It is important that the Ilossing layer deposition contains a high copper content, especially in the range of 60 to 75 % copper, the remainder being zinc. For this purpose, the electrolyte must be composed of:

(a) sodium cyanide 34 to 57 g / l (4.6 to 7.5 oz./gal.)

(b) sodium hydroxide 15 to 30 g / L (2 to 4.0 oz./gal.)

(c) Sodium Carbonate 30 to 90 g / L (4 to 12 oz./gal.)

(d) Total metal in solution including copper and zinc 22 to 45 g / L (3 to 6 oz./gal.), with the copper, as a percentage of the total, 68 to 85 % in the solution and the zinc, as a percentage of the total, be 32 to 15 % . This can be achieved by using zinc cyanide at about 37.5 g / l (5.0 oz./gal.) And copper cyanide at about 37.5 g / l (5.0 oz./gal.) V / earth. There is no need to include a brightener in the brass plating electrolyte such as dimethyl sulfamate or sodium polysulfide. The electroplated substrate is rinsed in room temperature water for about 1 minute.

6) A copper or copper and nickel layer approximately 0.0012 cm (.0005 ") is deposited. The copper layer can progressively in layers for example as the first layer (a) using a copper layer of 0.00012 cm

809849/1002

- 26 -

28 243 2 Q

(.00005 ") using an electrolyte with a general composition of 40 g / l (5.3 oz./gal.) CuCIT, 51 g / l (6.7 oz./gal.) NaCN, 30 g / l (4 oz./gal.) IJa ₂ CO ₇ and 60 g / l (8 oz./gal.) KNaC ₄ II ₄ O ₆ ^ H ₂ O, (b) Plating of an acidic copper layer from a copper sulphate and sulfuric acid Electrolyte which is about 0.001 cm (.0004 ") thick; and (c) plating a cyanide copper layer to a thickness of about 0.00012 cm (.00005") is formed, applying a post-formation rinse to each copper layer.

7) Electrodeposition of a high copper hardness brass layer approximately 0.00075 cm (.0003 ") thick containing copper in the range of 50 to 60 % . The coated substrate of the previous steps is placed in the electrolyte with the current applied, where the current density is o about 3 to 6 A / dm (30 to 60 amps./sq.ft.) and plating is carried out over a period of about 30 minutes to form this thickness , 5 g / l (3.5 oz./gal.), Free sodium cyanide 49 g / l (6.5 oz./gal.), Copper cyanide in an amount of 30 g / l (4 oz./gal.) Zinc cyanide in an amount of 19 g / l (2.5 oz./gal.). The substrate is also rinsed with water at room temperature for about 1 minute after this stage.

8) Electrodeposition of a copper layer approximately 0.00012 cm (.00005 ") thick from a cyanide copper layer to ensure optimal adhesion between the brass layer with 50 to 60% copper and the subsequent nickel layer. It is rinsed in water.

9) The substrate from the previous steps is then immersed in an acid containing 1% H ₂ SO ₄ (vol.-So) for a period of about 1 minute.

809849/1002

10) The previously plated substrate is then subjected to electrodeposited nickel plating to a minimum thickness of 0.00075 cm (.0003 "), the nickel being shiny and the nickel electrolyte preferably being 300 g / l (40 oz./gal. ) NiS0 ^ 6H ₂ 0.135 g / l

(18 oz./gal.) WiCl ₂ .6H ₂ O, 50 g / l (6 1/2 oz./gal.) H ₃ BO _{3 is built up} along with whitening and wetting agents, after which the nickel-plated substrate is then immersed in water is rinsed.

11) Finally, the substrate with an external chrome plating is about 0.000012 cm (.000005 ") thick in an electrolyte containing preferably 330 g / l (45 oz./gal.) CrO, and 3 g / l l (0.4 oz./gal.) H ₉ SO. when using a current density of about 18 a / dm equipped (175 ASF). The chromium plated substrate is then rinsed in a water etv / 88 to 93 ⁰ C hot and dried by blowing with hot air.

A number of test examples show the improved resistance to lateral corrosion in the embodiments according to the invention. The results of the tests are shown in Tables III and IV. The examples in Table III varied in the amount of copper deposited in the first layer of brass while the substrate consisted of 7029 aluminum alloy throughout. In Table IV, the substrate and embodiment were varied along with the percentage of copper deposited. It can be seen from these tables that in order to avoid lateral corrosion after 64 hours in the CASS test, the substrate must contain 4 to 6% zinc and the first brass layer must contain 60 to 75 % copper deposited. It also emerges, as can be seen from FIG. 9, that only that sample which contains 63 % copper had a sharply defined needle mark after 64 hours in the CASS test.

809849/1002

These samples were used to determine the corrosion behavior of clad aluminum alloy sheets or sections examined using the CASS test using the standard method listed in ASTM B-368. This test essentially consists in keeping the clad panels cleaned for increasing periods of time exposed to steam in a closed chamber. The steam is made up of a salt-copper solution that is applied to the required pH is adjusted with glacial acetic acid. The test cycles were each carried out for 16 hours. carried out and four such cycles were used. Before the test, each sheet or section was tested with an X-pattern scribed ^ the scribing was done by a Carbide cutting tool that cut through the cladding into the base metal. The sheets or sections were then cut through the crack and photomicrographs were taken of the corrosion progress, if any available.

Physical properties of the clad products

Figures 10-17 are photomicrographs of the cut marks in the 7029 aluminum sheets designated B-8, G-1, G-3 and G-7 in Table III. Figure 16, magnified 50 times, shows that 26 % copper in the brass causes significant side corrosion and delamination at 13, the peak of this side corrosion being enlarged in Figure 17. In FIG. 14, magnified 50 times, the sample contained 42 % copper in the first brass layer and this again allowed considerable lateral corrosion, the enlargement of the corrosion progress being evident in FIG. As shown in Figure 12, the use of 56 % Cu in the brass layer still allowed some side corrosion to progress from the crack along the brass. Only in Figs. 10 and 11 at 63 %

809849/1002

- 39- -

809849/1002

Ver
search- Brass layer
% Copper Separation copper
layer Table III Hours. to d.
Edge with the CASS test 32 hours ision Blah
sen-
0 48 Hours. Blah
sen-
0 64 Hours. ad
Kan
te BIa-
sen- sample bath 55.9 corrosion - Corrc ad
Kan
te - ivorr osion - corrosion 4mm 4-5mm G-1 58 52 no Results at the
At
crack - BIa-
sen- at the
At
crack 1 mm - at the
At
crack ad
Kan
te - at the
At
crack 2mm - G-2 53 41.8 no 16 1 mm no 2mm 4mm 1 mm - 4mm 3mm - 4mm 5mm - G-3 45 32.0 Yes 2mm - 2mm 2 mm 2mm 1 mm 3mm 5mm 15 gr.,
blow
and 3cl.
blow
4imn c / i G-6 29.5 26.0 Yes no no no 2mm 1 mm 2mm 3mm 2mm 5mm number
rich
oüasen
1 mm- G-7 20.3 63.0 1 mm no 10
Blah
sen
jev /.
1 mm 1 mm 2mm no 3mm 2mm no 3mm t
5 leinq keme B-8 75 63.0 Yes no Il number
rich
small"
blow
1 mm 2mm no ti 3mm 4mm It 4mm Il Il
- .. -K? C-8 75 no no no no ti no no no/ CQ
K) O
to
co
-P ^
co ti Il It ti Il 1 mm CD
IO

Table IV

sample 18th
18-3 Legie
tion Pre-treatment Top coating system Wi
Il and Cr
Il °, o Cu idclektro-
plated brass
c inn; layer
(1st shift) CASS-Ers: ebnisse
(visual examination
above)
(Words in inches) OK
Vs OK
1/4 from RD
RI 184 7016
7016 Alstan-Zinnein-
diving
Il It 52% brass,
Il Il Il OK
1/16 1/8 3/16 1/32
1/4 RM 7016 Il Il dd It It 1/16 OK OK 1/4 18th 7029 tf ti It dd Il OK 1/8 1/8 OK RV 21st 7046 Electroplated
Brass layer u.
Cyanide Cu layer
and acidic Cu layer Il Il It 1/16 OK OK 3/8 α 19th 7029 dd It Il ti 65 OK OK OK OK C.
cc 13th 7029 Il ft Il Il 58.3 OK OK i.C. <i / 32 α 7th 7029 It ti ti Il 65.8 OK OK <i / 32 OK . £ ■
CC 11 7029 ti Il tf ti 56.3 OK OK OK <i / 32 ^ * 6th 7029 Il Il If Il 58.7 OK OK <i / 32 <i / 32 C. 15th 7029 It Il ft It 56.3 OK OK OK 1/32 N 24 7029 π Il tf Il 65.8 OK OK OK i-0. 9 7029 It If II It 65 OK OK OK i-0. 2 7029 n It dd Il 58.7 OK 1/32 1/16 <i / 2> i2 18th 7046 ti dd It It 51 O / 32 1/32 1/32 1/16 18-1 7046 It ti Il ti 58.3 1/32 1/16 1/8 1/16 RZ 18-2 7046 π It dd ti 58.0 1/32 1/16 3/32 3/16 RZ 7046 It ti 58.0 1/32 1/8

Footnote: OK = "ok" or "irrelevant"

It follows from the foregoing that the fundamental teaching according to the invention can be used with great advantage for a variety of purposes.

Thus, it serves a process for the plating of aluminum-based objects, wherein (a) the object is selected and used from a recrystallized alloy with a content of 1 to 8% zinc on at least one of the surfaces to be plated, (b) the surfaces to be plated Surfaces can be cleaned practically free of any oxide film, (c) the object is immersed in an electroplating cell with applied voltage, the electrolyte of the cell being such that a brass coating is deposited directly on the object, the layer 60 to 75 wt. % Copper, and (d) a shiny decorative coating system, which consists of at least one of the metals nickel and / or chromium, is electroplated over this coated object.

Furthermore, there is a method for plating an object based on aluminum or magnesium, wherein (a) the object to be coated is selected and produced to a content between 1 and 8% zinc in the alloyed state, (b) after virtually complete removal of the oxide coating immediately and directly on top of the object a sub-layer of brass with a copper content in the range of 60 to 75% by weight of the deposited layer if the substrate consists of aluminum and 40 to 60% by weight if the substrate consists of magnesium , is electroplated and (c) a shiny decorative coating, which consists of at least one of the metals nickel and / or chromium, is electrodeposited over this coated object.

In these embodiments there are advantageously successive layers of copper and brass between the sub-layer

8098A9 / 1002

- 33 -

and the glossy decorative coating electrodeposited.

There is also a method of plating high strength aluminum alloys containing 4 to 8 % zinc and 1 to 4 % magnesium, wherein (a) after the oxide film has been virtually completely removed from the aluminum alloy article, a layer of brass containing thereon directly and immediately from 60 to 75% by weight of copper is electrodeposited in the deposited state and (b) a shiny decorative coating system, which consists of at least one of the metals nickel and / or chromium, is electrodeposited over it.

The teaching also provides a method for protecting an aluminum-based metal against corrosion, the aluminum metal containing 1 to 4 % zinc, a layer system of chromium on nickel on copper being electrodeposited on the aluminum metal, with the additional step of embedding an underlayer comprising copper with brass, the brass containing copper in the range of 45 to 75% by weight as deposited.

Furthermore, there is a method for plating an aluminum alloy with an overcoat system, wherein the alloy contains 4 to 8 % zinc and, after the aluminum object has been cleaned of aluminum oxide, a first brass layer to a thickness in the range of approximately 0.00012 to 0 immediately thereafter. 00025 cm (.00005 to .0001 ") is electroplated, the first brass layer containing sufficient copper to form a cathodic protection for the overlay system, which contains at least nickel and / or chromium, and to develop such a polarization that the current flow through any galvanic element between the aluminum article and the overlay system is reduced sufficiently to lower the level of corrosion, which is lower than the level between

809849/1002

Corrosion is common to copper and nickel.

There is also a process for electroplating nickel and chromium on an aluminum-based object, after which, after the aluminum coating has been virtually completely removed therefrom, the aluminum-based object is directly electroplated (a) using a three-layer system including a first layer of brass containing 60 to 75 weight percent copper as deposited, (b) a second layer of either copper or copper and nickel about 0.0012 cm (.0005 ") thick, and (c) a third layer of brass with a content of 50 to 60% by weight of copper as deposited, or a plating process for protecting an aluminum-based metal, the metal containing 4 to 8 % alloyed zinc and the system comprising chromium on nickel on copper on aluminum, wherein an electroplated layer of brass is interdeposited between the copper and aluminum metal, the brass Contains 60 to 75% by weight of copper.

Further, the teaching of a method for electroplating nickel and chromium onto an aluminum-based article can be found can be applied, after virtually complete removal of the aluminum oxide coating thereon the aluminum-based article by electroplating directly on top of a three-layer system consisting of (a) a first layer of brass with 60 to 75 wt.% copper as deposited, (b) a second layer of copper about 0.0012 cm thick (.0005 ") and (c) a third layer of brass with a content of 50 to 60% by weight copper in the deposited state is protected.

This results in objects of daily use, in particular bumpers for motor vehicles, whereby the objects have the following

809849/1002

the physical properties have: excellent adhesion of electroplated coatings which can be recognized by no peeling of any surface portion after the article by more than 90 ° mm with a radius from 3.1 to 12 (1/8 to 1/2 ") was bent, and which is evident from practically no lateral corrosion in the brass layer adjoining the aluminum after 64 hours in an accelerated copper-acetic acid-salt spray test.

809849/1002

Claims (12)

Λ I Process for the plating of objects based on aluminum, characterized in that (a) the article is selected and used from a recrystallized alloy with a content of 1 to 8 % zinc on at least one of the surfaces to be plated, (b) the surfaces to be plated practically free of any Cleaned oxide film, (c) the article is immersed in an applied voltage electroplating cell, the electrolyte of the cell being constructed so that a brass layer coating is deposited directly on the article, the layer containing 60 to 75 weight percent copper ^ and (d) a shiny decorative over this coated item Coating system, which consists of at least one of the metals nickel and / or chromium, is electroplated. 2. A method for plating an object based on aluminum or magnesium, characterized in that that (a) the object to be coated to a content between 1 and 8 % zinc is selected and manufactured in an alloyed state, (b) after practically complete removal of the oxide coating from the object on this immediately and directly thereon an underlayer of brass with a copper content in the 809849/1002 2024320 oil rich from 60 to 75% by weight of the deposited layer, if the substrate is made of aluminum, and 40 to 60% by weight, if the substrate is made of magnesium, is electroplated and (c) on top of this coated object a glossy decorative coating consisting of at least one of the metals Nickel and / or chromium is made, is electrodeposited. 3. The method according to claim 2, characterized in that successive layers of copper and brass are electrodeposited between the underlayer and the shiny decorative coating. 4. Process for the plating of high-strength aluminum alloys with a content of 4 to 8 % zinc and 1 to 4 % magnesium, characterized in that (a) after virtually complete removal of the oxide film from the aluminum alloy article thereon directly and immediately electrodeposited a layer of brass with a content of 60 to 75% by weight copper in the deposited state will and (b) a shiny decorative coating system, which consists of at least one of the metals nickel and / or chromium exists, is electrodeposited. 5. A method for protecting an aluminum-based metal against corrosion, the aluminum metal containing 1 to 4 % zinc, a layer system of chromium on nickel on copper being electrodeposited on the aluminum metal, characterized in that it comprises the additional step of embedding a sub-layer Comprises copper with brass, the brass containing copper in the range of 45 to 75% by weight as deposited. 609343/1002 6. A method for plating an aluminum alloy with an overlay system, the alloy containing 4 to 8 % zinc, characterized in that after cleaning the aluminum object from aluminum oxide immediately and directly thereon a first brass layer to a thickness in the range of about 0.00012 to 0.00025 cm (.00005 to .0001 ") with the first brass layer containing sufficient copper to form cathodic protection for the overlay system containing at least nickel and / or chromium and to form a polarization such that the current flow is reduced by any galvanic element between the aluminum article and the overlay system sufficiently to lower the level of corrosion, which is lower than the level of corrosion occurring between the copper and nickel. 7. A method for electroplating nickel and chromium onto an aluminum-based article, thereby marked shows that after practically complete removal of the aluminum coating therefrom, the aluminum-based article by electroplating (a) a three-layer system immediately thereafter including a first layer Made of brass with a content of 60 to 75% by weight of copper in the deposited Condition, (b) a second layer of either copper or copper and nickel about 0.0012 cm thick (.0005 ") and (c) a third layer of brass with a content of 50 to 60% by weight copper in the deposited state is protected. 8. A plating process for protecting an aluminum-based metal, the metal containing 4 to 8 % alloyed zinc and the system comprising chromium on nickel on copper on aluminum, characterized in that §09843 / 1002 an electroplated layer of brass is interdeposited between the copper and aluminum metal, the Brass contains 60 to 75 wt.% Copper. 9. Plating method according to claim 8, characterized in that the metal is aluminum-based is recrystallized. 10. Process for electroplating nickel and chromium to an aluminum-based article, thereby characterized in that after practically complete removal of the aluminum oxide coating thereon the article based on aluminum by electroplating a three-layer system from (a) a first directly thereon Layer of brass with 60 to 75 wt.% Copper in the deposited state, (b) a second layer of copper in one About 0.0012 cm (.0005 ") thick and (c) a third layer of brass containing 50 to 60 weight percent Copper is protected in the deposited state. 11. The commodity obtained according to claim 10, wherein a layer of pure copper and a second layer of brass are formed between the first layer of brass and the decorative coating system, the second layer of brass containing 50 to 60% by weight of copper. 12. commodity obtained according to claim 10, characterized in that the object has the following physical properties: excellent Adhesion of the electroplated coatings, which can be recognized by no peeling of any part of the surface there after moving the object by more than 90 ° with a 8098A9 / 1ÖÖ2 2S24320 Radius from 3.1 to 12 mm (1/8 to i / 2 ") bent, and due to practically no lateral corrosion in the brass layer adjoining the aluminum after 64 hours in an accelerated copper acetic acid salt spray test recognize there. 809840/1002